1. Field of the Invention
The present invention relates to a recording apparatus having a feed knob for conveying a recording sheet manually.
2. Related Background Art
A recording apparatus is shown wholly in FIG. 1, and a conventional mechanism for transmission of rotation in a sheet conveying system in the recording apparatus is shown in FIG. 2. FIG. 3 shows a connection between a feed knob and a recording sheet feed roller in the conventional transmission mechanism of FIG. 2. As shown in FIG. 2, the conventional transmission mechanism includes a feed knob 1 used for conveying a recording sheet manually and mounted on a shaft 2a of a sheet feed roller 2, and a feed motor as a driving source for normally drivingly rotating the feed roller 2.
The shaft 2a of the feed roller 2 has a D-cut end portion (FIG. 3) and the feed knob 1 has a mounting shaft portion having a corresponding D-cut hole formed therein, so that, when the feed knob 1 is mounted on the shaft 2a, a rotational torque from the feed knob can be transmitted to the feed roller 2. A depth or length that the knob is inserted onto the shaft 2a is regulated by a stopper ring 3 attached to the shaft 2a.
On the other hand, a driving force generated by the feed motor 4 is transmitted through a motor gear 5, transmission gear 6 and transmission gear 7 to a feed gear 8 to gradually reduce the speed of rotation from the feed motor. The feed gear 8 is coaxially and fixedly mounted on the shaft 2a of the feed roller 2 so that the feed roller 2 is rotated through the rotation of the feed gear 8. In this way, the rotation from the feed motor 4 is transmitted to the feed roller 2 through the reduction gear train to feed the recording sheet.
In FIG. 1, the recording sheet (not shown) is conveyed by the feed roller 2 in front of a recording head 9 mounted on a carriage 10 which can be shifted along a guide rod 11 by a carriage motor (not shown) through a timing belt 12 connected to the carriage. When the recording sheet reaches the recording position in front of the recording head 9, a leading edge portion of the recording sheet is held between an ejector roller 13 and a spur roller (not shown) in a spur guide 14. After recording is effected on the recording sheet through a scanning operation of the recording head 9 by means of the carriage 10, the recording sheet is conveyed by rotating the feed roller 2 by means of the feed motor 4.
The technique that both the manual sheet feed by means of the feed knob and the automatic sheet feed by means of the feed motor are used in the recording apparatus, as mentioned above, is already known as disclosed in the Japanese Patent Application Laid-Open No. 59-182766 and the Japanese Patent Application Laid-Open No. 59-184685 (corresponding to U.S. Pat. No. 4,733,250). Incidentally, U.S. Pat. No. 4,733,250 teaches a technique that a sheet feed and an up-down shift of the recording head are carried out by means of the same motor by switching a clutch according to the position of a carriage.
However, in the past, in the recording sheet conveying system of the recording apparatus, since the holding force of the feed motor was maximum when the feed knob was manually rotated in the same direction as a driving direction of the feed motor while driving the feed motor and since the driving speed from the feed motor was being reduced by the transmission gear train, the feed gear 8 was subject to a considerably large torque. Consequently, since the considerably strong force acted on the engagement portion between the transmission gear 7 and the feed gear 8, there arose a problem that the teeth of these gears were deformed and/or damaged.
On the other hand, recently, a sheet conveying apparatus with a short pitch and an improvement in accuracy of sheet conveying has been requested according to the tendency of the recording with high density. In this case, the speed ratio in the sheet conveying system must be increased. However, the more the speed ratio is increased, the more the force acting on the gears is increased.